The present invention relates to an elevator controlling apparatus which employs variable-voltage and variable-frequency control (referred to as "VVVF control", hereinafter) and, more particularly, to the handling of electric power regenerated by the elevator hoist motor.
FIG. 4 shows a known apparatus for controlling an elevator.
Referring to FIG. 4, a converter 1 is constituted by a diode rectifier which converts the alternating current from three-phase AC mains R, S, T into a direct current. A smoothing capacitor 2 is connected to the DC side of the converter 1. A known PWM type inverter 3 is also connected to the DC side of the converter 1. The inverter 3 is constituted by a transistor 3a and a diode 3b in this example such as to convert a constant DC voltage into a VVVF AC voltage by pulse-width control. A three-phase induction hoist motor 4 is connected to the inverter 3. A hoist 5 is connected to the motor 4 through a shaft 4a. A brake 6 is adapted to brake the hoist 5. A main rope 7 is passed over the hoist 5. A cage 8 and a counterweight 9 are respectively connected to opposite ends of the main rope 7. The reference numerals 10 and 11 respectively denote a speedometer and a current transformer which detects the current flowing through the motor 4. A controller 12, to which signals from the speedometer 10 and the current transformer 11 are input, controls the voltage and frequency of the output of the inverter 3. A resistor 13 is provided to consume electric power which is regenerated by the motor 4, while a series-connected switching transistor 14 controls the on/off operation of the resistor 13 by either blocking or permitting current flow therethrough. A regenerated power-detecting means in the form of a voltage detector 15 is adapted to detect the voltage across the smoothing capacitor 2 via leads or probes 15a. The means 15 is actuated when the voltage across the smoothing capacitor 2 exceeds a predetermined value such as to make the transistor 14 conductive, thereby turning on resistor 13. The regenerated power detecting means 15 has heretofore been constituted by an overvoltage detector which is actuated whenever electric power is regenerated. (An apparatus similar to the above-described one has been shown in the specification of Japanese Patent Laid-Open No. 163276/1984).
The operation of the elevator controlling apparatus shown in FIG. 4 will now be described.
Whether an elevator is operating in a powered-running state or in a regenerative-running state is decided by the relationship between the weight of the cage 8 including passengers, and that of the counterweight 9 and by the running direction. More specifically, when the cage 8 is raised while bearing a load which corresponds to its fixed capacity, the motor 4 is in the powered-running state. In such as case, the motor 4 is supplied with electric power from the converter 1, and there is no possibility of the overvoltage detector 15 being actuated. On the other hand, when the cage 8 is lowered while bearing a load corresponding to its fixed capacity, the motor 4 is in the regenerative state.
Since the converter 1 is constituted by a diode rectifier, it is not possible to return the regenerated power to the power source R, S, T. For this reason, when electric power is regenerated, the voltage across the smoothing capacitor 2 rises and actuates the overvoltage detector 15 such as to make the transistor 14 conductive. When transistor 14 is conductive, current flows through the resistor 13 which dissipates or consumes the regenerated power. Since the regenerated power is thus consumed or absorbed, cage 8 is run at a predetermined speed without any fear of its being lowered at an excessive speed.
However, the resistor 13 is generally installed in a machine room (not shown) where the motor 4 and other devices may be housed. As a consequence, the heat generated from the resistor 13 undesirably raises the temperature of the machine room. When the capacity of the motor 4 is relatively small, this heat problem is not extremely serious. However, as the speed or carrying capacity of the cage 8 increases, the capacity of the motor 4 must be increased. As the rated load or capacity of the motor 4 is increased, the power regenerated thereby also increases, and the generation of heat in the machine room also increases.
Consequently, the air-cooling capacity required to cool the machine room also undesirably increases, which fact disadvantageously involves an increase in the consumption of energy in the building as a whole.
Another known elevator controlling apparatus is shown in FIG. 5.
In FIG. 5, the same members or portions as those in FIG. 4 are denoted by the same reference numerals. A converter 20 is constituted by a thyristor rectifier. The converter 20 is fired by a firing circuit 20a. A regenerative inverter 21, which is adapted to return the regenerated power to the power source R, S, T, is constituted by six thyristors 21t. A firing circuit 21a is adapted to fire the regenerative inverter 21. A reactor 22 is connected to the DC side of the regenerative inverter 21. The reactor 22 is employed to protect the regenerative inverter 21 when the converter 20 becomes inoperative as a result of an undesirable stoppage of current from the power source R, S, T. An autotransformer 23 is provided to make reliable the commutation of the regenerative inverter 21. The voltage of the autotransformer 23 on its regenerative inverter 21 side is slightly higher than the voltage of the power source R, S, T.
In the elevator controlling apparatus shown in FIG. 5, the overvoltage detector 15 also is not actuated when the motor 4 is in a powered-running state, in a manner similar to that of the apparatus shown in FIG. 4. As a consequence, the firing circuit 20a actuates the converter 20 such as to supply electric power. On the other hand, when the motor 4 is in a regenerative state, the overvoltage detector 15 is actuated such as to make the firing curcuit 20a inoperative and to cause the firing circuit 21a to fire the regenerative inverter 21. This firing allows the regenerated power to be returned to the power source R, S, T via the regenerative inverter 21 and the autotransformer 23.
In the elevator controlling apparatus shown in FIG. 5, the thyristors 21t are required to possess a capacity large enough to return the regenerated power to the power source R, S, T, which fact disadvantageously involves an increase in cost.
Another known regenerated power handling apparatus has been disclosed in the specification of Japanese Patent Laid-Open No. 154380/1983 (U.S. patent application Ser. No. 470,955, filed Mar. 1, 1983). This regenerated power handling apparatus is arranged such that, in a first stage of regeneration of power, the regenerated power is employed as a power source for various controllers of the elevator, and as the regenerated power further increases in amount, it is also consumed by a resistor, thereby eliminating any need to provide an inverter for regeneration of electric power.
In practice, however, there are cases where it is not possible to use the above-described arrangement wherein no power regeneration inverter is employed. Therefore, it is not always possible to say that such an arrangement is adequate for practical use.
Further, utilization of regenerated power at a power failure is disclosed in the specification of U.K. Patent Application Publication No. GB No. 2,111,251A (U.S. patent application Ser. No. 440,350, filed Nov. 9, 1982). According to the disclosure, at the time of a power failure various control circuits for an elevator are driven by the use of regenerated power such that the elevator is stopped at the nearest floor.
In an apparatus having the above-described arrangement, however, the regenerated power in a normal operation is handled in a regenerative inverter and returned to a power source. In a consequence, this apparatus also disadvantageously requires a regenerative inverter which is high in cost, such as that described in relation to FIG. 5.
U.S. Pat. No. 4,503,940, assigned to the assignee of this application, disclosed a VVVF elevator control system in which the regenerated power is normally returned to the A.C. mains through a regenerative inverter. However, when an emergency generator becomes the A.C. source upon failure of the main A.C. source, the regenerative inverter is blocked and the regenerated power is absorbed or consumed by a resistor.
As will be understood from the above description, known elevator controlling apparatuses have suffered various problems, that is, an excessive rise in the temperature in the machine room in the case where regenerated power is consumed in a resistor, and an increase in the cost because of the regenerative inverter in the case where the regenerated power is return to the power source.